For most of the election cycle, Democratic strategists were optimistic they could hold the House because of their arsenal of opposition research. But Democratic attacks failed to bring down enough Republican challengers to keep the majority.

Democrats thought GOP challengers were simply too flawed to be acceptable alternatives to voters who wanted change. But as Republicans learned in 2006 and 2008, the messenger and the audience matter just as much, if not more, than the message when it comes to political attacks.

“If you were in a red district, nothing worked,” according to one veteran Democratic strategist, reluctantly recalling the most recent elections.

In Tennessee’s 8th district, Democrats tried to use Scott DesJarlais’ divorce records to paint the Republican as an emotionally unstable man who threatened his wife and petitioned to have his child support payments reduced. Democrats in Georgia’s 8th district called for GOP nominee Austin Scott’s divorce records to be unsealed, and national Democrats spread rumors about its contents.

In Florida’s 25th, Democrats described Republican David Rivera’s “troubling history of going to great lengths to hide a violent past,” according to an Oct. 1 news release. Democrats also tossed around domestic violence accusations against him and an incident where Rivera allegedly forced a truck off the road.

And in Ohio’s 16th, Democrats accused Republican Jim Renacci of “placing profits before safety” by endangering his nursing home residents to make more money and highlighting the story of a woman who died in a facility he owned.

Sen. John McCain (R-Ariz.) won all four Congressional districts in the 2008 presidential election, and all four Republicans were elected to Congress this year. Scott won by 5 points, Renacci and Rivera by 11 points, and DesJarlais by a whopping 20 points.

The Renacci attack is reminiscent of 2008, when Republicans accused then-Democrat Parker Griffith of under-medicating cancer patients in order to make more money off of them. Griffith won that competitive open-seat race by 4 points.

But even in more competitive districts that President Barack Obama carried by less than 10 points two years ago, Democratic attacks often fell on deaf ears.

“Frank Guinta fled the scene of a bar brawl, stepping over the victim’s body on his way out the door,” Democrats accused of the GOP nominee in New Hampshire’s 1st district.

All three Republicans defeated Democratic incumbents this fall, and only Farenthold’s race was close.

“It’s harder to disqualify candidates in a national election,” the Democratic source said.

Voters tuned out the Democratic attacks because they were frustrated with the party in power. In 2006 and 2008, the same attacks would have destroyed these GOP candidates.

“People were more willing to take it from the press than to take it from us,” the source added.

In handful of races, the local media drove the narrative on the attacks against GOP nominees.

“Jeff Perry was nearby when [Officer] Scott Flanagan illegally strip searched me. Perry knew what Flanagan did, he had to hear me screaming and crying,” Lisa Allen told the local media about the GOP nominee in Massachusetts’ 10th district.

Allen’s statement was in relation to an incident in 1991, in which Allen was illegally strip-searched by Flanagan, a former Wareham Police Department officer. Perry was sergeant of the department at the time. Flanagan was later convicted of indecent assault on a child in relation to the incident. “It upsets me that Jeff Perry can run for Congress after what he did to me when I was fourteen years old,” she said in her statement.

In Iowa’s 3rd, Democrats pounced on almost decade-old allegations that GOP nominee Brad Zaun harassed his ex-girlfriend. And in Ohio’s 13th, wealthy car dealer Tom Ganley’s surprising campaign to defeat Rep. Betty Sutton (D) came to a screeching halt when accusations of sexual assault surfaced during the race.

Democrats retained all three districts, but they were also in friendlier territory, since Obama won each district by at least 10 points. It appears Democratic attacks worked best to motivate Democrats or to persuade left-leaning independent voters.

But sometimes the attacks either gained more attention inside the Beltway than in the district or the negative story lasted for days rather than weeks or months.

Some Republicans think the potency of the attacks had more to do with an effective defense.

“You cannot sustain these kinds of attacks unless you have the campaign and messaging infrastructure to combat them,” said Ken Spain, communications director for the National Republican Congressional Committee.

GOP strategists were consistently critical of Zaun for his lack of fundraising. Ganley effectively pulled the plug on his own campaign when the allegations surfaced in his race. Meanwhile, candidates such as DesJarlais, West, Renacci and Guinta pushed through when attacked.

Not every good campaign was rewarded. GOP strategists gave credit to Keith Fimian for the campaign he ran against Rep. Gerry Connolly (D) in Virginia’s 11th district, but the GOP nominee told a reporter in late October that the 2007 massacre at Virginia Tech could have been avoided if the students had been “packing heat.”

“There was no margin for error, and he committed an unforced error,” said one GOP operative familiar with the race. Fimian lost the race by fewer than 1,000 votes in a district that Obama won by 15 points in 2008.

Good campaign or not, the nature of the district appears to be the best indicator of whether an attack will stick in a national election.

In Pennsylvania’s 10th district, former U.S. Attorney Tom Marino struggled to raise money and was hounded by Democrats and the media for his connection to a convicted felon.

But the Republican was running in a district that McCain won by 9 points and had the luxury of a cheap media market where the NRCC could come in heavy with TV advertising. Marino defeated Rep. Christopher Carney by 10 points, even though his negatives were higher than the Democratic Congressman’s.

Democrats lost the House, but they don’t think the conversation is over. Case in point: A judge delayed a hearing that was scheduled for next week about Scott’s divorce records, an issue Democrats have tried to keep on the radar screen for reporters.

“For the most part, voters did not take a close look at the Republicans they elected — and in turn, there are numerous new Members with long records of reckless positions and questionable behavior that we will be able to exploit over the next two years,” said Jon Vogel, executive director of the Democratic Congressional Campaign Committee.